The present invention relates to apparatus for developing latent electrostatic images on dielectric carrier or receptor sheets. More particularly, the invention relates to improvements in developing apparatus of the type wherein a carrier sheet travels with respect to a stationary electrode and its image-bearing surface is contacted by a developing fluid which contains toner particles.
Commonly owned U.S. Pat. No. 4,013,356 granted Mar. 22, 1977 to Bestenreiner et al. (to which reference may be had, if necessary) discloses a developing apparatus wherein the gap between the electrode and the travelling carrier sheet receives fresh developing fluid by way of fluid-admitting ports which are machined into the electrode. Spent fluid is removed by way of evacuating ports in the electrode. The gap between the moving carrier sheet and the electrode is divided into several sections each of which includes a fluid-admitting port and an evacuating port. The ports are actually narrow slits extending transversely of the direction of movement of the sheet and are inclined with respect to each other. Fresh fluid which issues from the fluid-admitting ports is introduced in such a way that it has a component of movement in the direction of travel of the carrier sheet, and the inclination of the evacuating ports is just the opposite. The aforediscussed inclination of the ports is intended to reduce turbulence in the gap between the electrode and the carrier sheet.
A drawback of the just described apparatus is that certain sections of the gap are not used for development of the latent image. Therefore, the length of the gap, as considered in the direction of movement of carrier sheets, greatly exceeds the combined length of the aforementioned developing sections. Otherwise stated, certain sections of the gap do not receive any developing fluid. Moreover, the evacuation of spent fluid from the corresponding orifices necessitates the expenditure of energy in addition to that energy which is needed to force fresh developing fluid into the gap via fluid-admitting ports.